The vast majority of
mental and sensual stimulants are as such learned (the
conditioned reflexes, incl. Pavlovian ones).The tactile
stimulants applied to specific erogenous zones and the pheromones can trigger the involuntary sexual
arousal without previous learning.

Non-sexual triggers of sexual arousal which are beyond control

Misattribution of arousal: stimulus-induced release of adrenaline - bodily reaction to adrenaline
- emotion attributed falsely to recognizing the initial stimulus as
attractive. The actual attribution of arousal being incorrectly accredited to the
wrong source. An emotional experience that is inaccurately attributed
to the wrong reason rather than the actual cause. The role of epinephrine, aka adrenaline.
Involuntary Exercise Induced Orgasm (IEIO), coregasm (while performing a core exercise during a work-out)Kegel Induced Orgasm (KIO)

Last Tango in Paris (Italian: Ultimo tango a Parigi) by Bernardo
Bertolucci, 1972. JEANNE (Maria Schneider placing her hands over area
where she experienced her first orgasm triggered by entirely non-sexual
stimulus.

PAUL (Marlon Brando): When did you first come? How old were you?JEANNE (Maria Schneider): The first
time? I was really late for school. I started running and it was
downhill. All of a sudden, I felt a strong sensation here. (posing her hands over her lower abdomen, above).
So I ran and ran and I came as I ran. The faster I ran, the better it
was and the more I came. A couple of days later, I tried to do it
again, but no luck.